The present invention relates to a photosensitive material and, more particularly, to a photosensitive material in which a radiation sensitive composition is distributed in a plurality of capsules and exposure of the composition controls the release of the internal phase from the capsules and the activation of an image forming agent. More particularly the present invention relates to a process for improving the sensitivity of these materials by performing a non-imaging exposure which sequesters oxygen.
Photosensitive materials of the aforementioned type are the subject of commonly assigned U.S. application Ser. Nos. 320,356 and 320,643 filed Nov. 12, 1981 now U.S. Pat. Nos. 4,399,209 and 4,440,846, respectively. Images are formed by image-wise exposing these materials to actinic radiation and rupturing the capsules. Where the capsules contain a radiation curable composition, such as polyethylenically unsaturated compounds, the capsule contents become more viscous in the exposed areas and remain less viscous in the unexposed areas. Thus, upon appropriately applying pressure to the image-wise exposed sheet, the capsules in the image areas (which correspond to the unexposed and partially exposed areas) rupture and release their contents whereas the capsules in the non-image areas do not. Release of the internal phase image-wise activates an image forming agent associated with the capsules which proceeds with the formation of an image upon transfer, reaction with a developing agent, or otherwise.
Other types of imaging systems based on photosensitive encapsulates are known.
Berman, U.S. Pat. No. 3,219,446 discloses a transfer imaging process in which azo-blue-"B" black dye is encapsulated with a photocross-linkable polymer or a photopolymerizable monomer as a fluid droplet-containing film or fluid droplet-containing microcapsules. In this system, imaging is accomplished by image-wise exposing a layer of the encapsulate to electromagnetic radiation to cross-link the polymer or polymerize the monomer. This is stated to cause the liquid in the exposed capsules to assume a non-liquid, rigid condition. Images are formed by transferring the dye from the still liquid capsules to a receiving sheet by the use of pressure. Experimentation with the Berman system has shown that it has a very low sensitivity (i.e., requires a comparatively intense exposure to form an image) and provides poor image contrast.
Phillips, U.S. Pat. No. 3,700,439 discloses a photocopy process wherein Michler's ketone is encapsulated in a conventional manner and provided as a layer on a support. Michler's ketone itself is not a color former, but patterned irradiation of the ketone in the capsules converts the ketone to a colorless, acid colorable, dye precursor. When this dye precursor is subsequently contacted with an acid developer, such as acid clay, a visible image is obtained. Phillips discloses both a system in which the exposed imaging sheet is calendered face-to-face with an acid coated receiving sheet to form images and a system wherein the acid developer is on the same surface as the capsule coating so that after rupturing the capsules there is development without transfer.
Levy, U.S. Pat. No. 4,149,887, relates to a capsular imaging material having a photoconductive internal phase which is exposed in an RF field. Exposure increases the conductivity of the internal phase and causes the capsule to heat, swell and then rupture in the image areas. The capsules may contain color precursors which form images by reacting with a developing agent.
The present invention is directed to improving the sensitivity of capsulated imaging materials employing radiation sensitive compositions by conducting an oxygen sequestering exposure.